How To Know When Your Computer’s CMOS Battery Is Dead

By: Contributors  | 
A scientist checking the battery compartment of an electronic device in his hand
A CMOS battery provides power even when the computer is off and allows the CMOS to save all the settings Catherine Falls Commercial / Getty Images

All personal computers have a small battery on the motherboard that provides power to the Complementary Metal Oxide Semiconductor (CMOS) chip, hence the name CMOS battery. This CMOS battery powers the chip, holding information about the system's configuration, such as the hard disk, date and time, etc. It provides power even when the computer is off and allows the CMOS to save all the settings. You can expect the CMOS battery to last for up to five years. The more your computer is used, the longer the battery will last.


How Do You Know That Your CMOS Battery Is Dying?

Here are some tell-tale signs that your battery is dying:

  • The keyboard acts up with keys and the cursor not responding.
  • Invalid configuration will appear on your screen.
  • Run Setup appears on your screen.
  • Press F1 to continue appears on your screen.
  • Invalid drive specification appears on the screen after you've pressed F1.
  • Clock Error or Clock Message appears on your screen.
  • The clock on the computer loses time.
  • The computer is constantly showing the wrong date.

Should you experience any of these symptoms, it's likely time to change the battery in your computer. If you don't change the battery, the battery will die. Your battery is dead when your screen is blank and you have thus lost your CMOS memory.


Recognizing the Need for a CMOS Battery Replacement

When your desktop computer or laptop starts experiencing the symptoms of CMOS battery failure, it's a clear indication that the CMOS battery, often a lithium battery, is nearing the end of its lifespan. When a CMOS battery fails, it can lead to difficulties in booting your computer, as the BIOS settings, which are essential for the operating system to communicate with the hardware, are lost or reset.


Replacing a CMOS Battery

Replacing an old battery with a new one is a straightforward process but requires careful handling to avoid damage to your computer's motherboard or other components. Here’s the basics to remove the battery and replace it:

  1. Safety First: Before starting, ensure the computer is turned off. Unplug all cables and peripherals to prevent any electrical accidents or damage to the ports.
  2. Access the Battery: For a desktop computer, you'll need to open the case to access the motherboard. In a laptop, the location of the CMOS battery might be under one of the panels on the bottom or, in some cases, under the keyboard.
  3. Remove the Old Battery: The CMOS battery is usually held in place by a clip. Gently push the clip aside to release the battery. Be careful not to use excessive force that could damage the motherboard.
  4. Insert the New Battery: Make sure the new lithium battery is the same type as the one you're replacing. Insert it into the battery socket, ensuring the positive side is facing up.
  5. Reassemble and Test: Once the new battery is in place, reassemble your computer and re-screw the computer or laptop casing. Reconnect all cables and peripherals, then turn on your computer. Check if the BIOS settings need to be configured and if the clock retains the correct time and date.


After Replacing the CMOS Battery

After you replace a dead CMOS battery, you might need to re-enter the BIOS settings. This is because the BIOS may revert to its default configuration, which may not be optimal for your specific hardware setup or the way you use your computer. Familiarize yourself with entering the BIOS setup (usually by pressing a key like F2, Delete, or Esc during booting) and adjust the settings as needed.

We updated this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.


Frequently Answered Questions

How long do computer CMOS batteries last?
Generally, computer CMOS batteries last 3-5 years.
Can a dead CMOS battery affect the operating system?
Yes, a dead CMOS battery can cause issues with the operating system by resetting the BIOS settings, which in turn can affect the system's ability to detect and configure hardware.
Is it necessary to replace the CMOS battery in laptops as well as desktop PCs?
Both desktops and laptops use a CMOS battery, though the replacement process can be more challenging in laptops due to their compact design. Always consult your laptop’s manual and consider consulting a professional.
How do I know which lithium battery to buy as a replacement?
Most computers use a CR2032 lithium battery, but it's best to check the old battery's model before purchasing a new one. Ensure you buy the exact match to avoid compatibility issues.
Are there any risks involved in replacing the CMOS battery myself?
While replacing the CMOS battery is generally safe when done carefully, there's a risk of damaging the motherboard if you apply too much force or accidentally discharge static electricity.